This invention relates to a filter temporarily positionable in a lumen, for example, the lumen of an artery, for trapping and removing particles from a fluid flowing through the lumen while allowing the fluid to flow relatively unimpeded through it.
Various vascular procedures, such as the removal of a stenosis occluding an artery or the positioning of a stent graft to reinforce the weakened artery wall at an aneurysm, tend to dislodge particles or emboli from the wall of the artery. The dislodged emboli become entrained in the blood stream flowing through the lumen of the artery. If allowed to remain in the blood flow, the emboli are carried through the vascular system until they lodge in a blood vessel thereby forming a blockage or embolism. Depending upon the size and/or volume of the emboli and where in the vascular system they lodge, the consequences of an embolism can be extremely serious, resulting, for example, in the sudden cessation of blood flow to an extremity, an organ, such as a kidney, the brain or the heart.
There is clearly a need for a filter which can be temporarily positioned in the lumen of an artery downstream from the point where a medical procedure is taking place which may dislodge emboli from the artery wall. The filter should trap emboli above a predetermined size but allow the blood to flow through relatively unimpeded. The filter should be removable from the artery after the procedure is complete and no further emboli are dislodged, the filter bringing all of the trapped emboli with it out of the vascular system.
The invention concerns an intraluminal filter positionable within a lumen for separating entrained particles from a fluid flowing within the lumen. Although other applications are envisioned, the filter is particularly well suited for vascular use.
In its preferred embodiment, the intraluminal filter according to the invention comprises a plurality of filamentary members interlaced to form a basket. The basket has an upstream portion and a concave portion arranged to face the upstream portion. The upstream portion has openings sized to allow the fluid and the entrained particles to flow through and into said concave portion when the upstream portion is oriented upstream within the lumen. The concave portion comprises a filter element and has openings of predetermined size smaller than the first named openings. The openings of the concave portion are sized to capture the entrained particles while allowing the fluid to flow therethrough.
In a preferred embodiment for vascular use, the intraluminal filter also has a means for biasing the basket from a first shape state to a biased second shape state. The first shape state has a first diameter sized to allow the basket to slidingly fit within the bore of a catheter positionable within said lumen. The biased second shape state has a second diameter substantially larger than the first diameter, the biased second shape state being sized to allow the basket to sealingly interfit within the lumen.
There are various biasing means contemplated. For example, the biasing means may comprise selected ones of the filamentary members. These selected filamentary members being resilient and biased by internal elastic forces to expand the basket into the biased second shape state when the basket is released from the catheter.
In addition to or instead of the selected filamentary members, the biasing means may comprise a plurality of supplemental filamentary members. The supplemental filamentary members are elastic and oriented to compress the basket into the biased second shape state. The supplemental filamentary members are under tension when the basket is in the first shape state and compress the basket to bias it into the second shape state upon release of the basket from the catheter.
Another alternate biasing means comprises an elongated elastic member having one end attached to the upstream portion and the other end attached to the concave portion of the basket. The elastic member is under tension when the basket is in the first shape state to bias the upstream portion toward the concave portion in order to expand the basket from the first to the second shape state.
Preferably, the filamentary members are interlaced by braiding, a method of interlacing which allows the basket to readily assume the first and second shape states. It is convenient to form the basket by braiding the filamentary members into a tube having a predetermined length. The tube has oppositely arranged ends which are gathered and cinched to form the basket. Preferably, one of the ends forms the second portion of the basket which is not obstructed by the second filamentary members, thus, forming the openings at that end.
In an alternate embodiment, the filter includes a plurality of projections extending angularly outwardly from the filter. The projections are interengagable with the internal surface of the lumen and prevent downstream movement of the filter. The projections are arranged to point in the downstream direction to allow them to readily disengage from the lumen when the filter is moved in an upstream direction for retraction of the filter into the catheter.
The projections can be conveniently formed by cutting some of the selected filamentary members forming the basket at points adjacent to the concave portion of the basket. The projections adjacent to the first portion of the basket are relatively unrestrained and project angularly outwardly. The complementary end portions at the concave portion of the basket which result from the cut filamentary members are restrained by filamentary members forming the filter element and, thus, do not tend to extend outwardly from the filter. Preferably, the cut filamentary members forming the projections are present in a one to one ratio with the uncut filamentary members forming the basket.
It is advantageous to attach a flexible tether to the unobstructed end of the basket. The tether has a predetermined length and is extendable through the catheter for allowing the intraluminal filter to be manually withdrawn from the lumen into a catheter bore, for example, after completion of a surgical procedure when the filter is no longer required. The filter, along with the captured emboli, are then removed from the lumen when the catheter is removed.
A preferred method of forming an intraluminal filter according to the invention comprises the steps of:
(a) braiding a plurality of flexible, resilient filamentary members into a relatively open mesh forming an elastically deformable tube, the filamentary members providing a radial bias to the tube, urging the tube to assume a predetermined length and diameter;
(b) interbraiding a multiplicity of yarns with the first filamentary members to form, with the filamentary members, a surface having a predetermined porosity, the surface comprising the filter element or means;
(c) gathering each end of the tube and cinching each end together to form an elastically deformable basket;
(d) removing the yarns from a portion of the basket at one end of the tube, thereby forming openings at the one end which allow the fluid and particles to flow into the filter; and
(e) attaching the yarns to the first filamentary members adjacent to the unobstructed portion of the basket.
Although the steps of removing and attaching the yarns can be accomplished in any of several ways, it is preferred to use a laser to ablate the multifilament yarns from the portion of the basket which is to be unobstructed and use the same laser to heat seal the yarns to the filamentary members adjacent to the unobstructed portion of the basket. The laser allows for pinpoint accuracy in targeting the yarns to be removed and heat sealed.
It is an object of the invention to provide a filter positionable within the lumen of an artery.
It is another object of the invention to provide a filter having a filter element of braided filamentary members to capture emboli above a certain size entrained with the blood in the artery.
It is yet another object of the invention to provide a filter which is elastically collapsible into a first shape state having a diameter sized to permit the filter to slidingly interfit within a catheter bore for positioning the filter within the artery lumen.
It is still another object of the invention to provide a filter which is self-expanding into a second shape state having a second diameter substantially larger than the diameter of the first shape state, the second diameter being sized to allow the filter to sealingly interfit within the artery lumen.
It is again another object of the invention to provide a filter which is collapsible from the second shape state to the first shape state by withdrawing the filter into the catheter bore for removing the filter from the artery lumen.
These and other objects will become apparent from a consideration of the following drawings and detailed description of the invention.